It is well known in the art to determine the pH in body fluids by using an electrode cell assembly and immersing the measuring electrode into a sample of the bodily fluid. The pH is known to be the symbol for the negative logarithm of the H+ ion concentration. The pH value of the blood makes it possible to estimate the carbon dioxide level of the blood, for example. The increased carbon dioxide concentration in the blood indicates that the organs of the body are not being provided with enough oxygen, which can ultimately prove harmful.
It is also known in the art to measure tissue pH in myocardial tissue. Measurement of pH in myocardial tissue has been used to determine the presence of myocardial ischemia, as indicated by a decrease in pH. During cardiac surgery, the aorta is cross clamped and the myocardium is deprived of its blood and nutrient supply. To avoid potential damage to the heart, the pH of the myocardium can be monitored to determine tissue acidosis and thus the onset of myocardial ischemia.
There is an ongoing need, however, for further improvements in methods for diagnosing and treating ishemic tissue.
While ischemia or tissue acidosis, in cardiac tissue has been measured, methods to prevent and/or reverse cardiac acidosis were unknown. Surgeons did not know how to reverse tissue acidosis once discovered. The present invention relates to a method of using tissue pH measurements to diagnose ischemia and/or gauge the conduct of an operation by determining whether a site is ischemic. The current invention also provides methods by which tissue acidosis can be corrected once discovered.
The present invention relates to pH-guided management of tissue ischemia or the use of pH measurements of tissue as a system for controlling diagnostic and/or surgical procedures. A preferred embodiment of the invention relates specifically to an apparatus and method which is applicable to patients undergoing cardiac surgery. It employs a tissue electrode and monitor and comprises a series of steps that in a preferred embodiment are aimed at achieving a homogeneous distribution of cardioplegic solution during aortic clamping, and at insuring adequate revascularization of ischemic segments of the myocardium. The method using pH-guided myocardial management guides the conduct of operations, prevents damage to the heart, extends the safe period of oxygen deprivation, and improves the outcome of patients undergoing heart surgery.
The use of the pH-guided myocardial management method to identify ischemic segments of a myocardium can provide a user with options for specific courses of conduct, both during and after, the surgical procedure. These options include: effecting an optimal delivery of preservation solutions to the heart to reduce ischemia, assessing the adequacy of coronary revascularization following a heart surgery procedure, identifying viable but nonfunctioning heart muscle, prompting changes in the conduct of the surgical procedure, monitoring the pH of the heart muscle post-operatively and evaluating the efficacy of newer myocardial protective agents.
There are several methods of delivery of a pH electrode, used in pH-guided myocardial management, to a site of interest. The electrode can be delivered manually by the user. The electrode can also be delivered by a catheter through a percutaneous incision. The electrode can also be delivered by an endoscope, a colonscope or a laparoscope to a site of interest. Thus, in a preferred embodiment of the invention, the method can be applied to other tissue measurements such as brain tissue, kidney tissue, musculo-cutaneaus flaps or the small or large intestines. In another embodiment, the pH of transplanted organs, such as liver or kidney, can be measured to assist in the diagnosis and/or treatment of rejection since acidosis is an early sign of rejection.
Other methods can also be used to measure pH, including, in certain applications, surface pH measurements, magnetic resonance measurements, or optical methods using fiber optic probes.
When a user has found that tissue acidosis is present at a site of interest, the user can effect an optimal delivery of preservation fluids, or cardioplegia fluids, to the heart to raise the pH of the site. Several methods of providing optimal delivery of the cardioplegia solutions to the site are available to the user. These methods include: altering the flow rate of the preservation fluid, altering the temperature of the fluid, altering the site of delivery, repositioning the tip of the catheter, selectively directing the preservation fluid through the manifold, applying direct coronary artery pressure on the proximal portion of the artery, occluding the left main coronary artery with a balloon catheter, inflating the balloon of a retrograde coronary sinus catheter, administering a bolus of cardioplegia through the orifice of a right coronary artery and accelerating a surgical procedure.
When a user has found that tissue acidosis is present at a site of interest, the user can also prompt changes to the conduct of the surgical procedure to raise the pH of the site. Several methods of changing the surgical procedure are available to the user. These methods include: determining the need for revascularization of a specific segment of the myocardium, changing the order of revascularization, providing for additional revascularization, changing the operation or the surgeon to reduce ischemic time, canceling an operation and delaying the weaning of a patient from cardiopulmonary bypass.
The pH electrode itself can have a cable connected to a silver wire where the silver wire is an Ag/AgCl (silver/silver chloride) wire. The cable and wires are encased in a housing which is encased in shrink tubing. The electrode has a glass stem which houses the silver wire, a thermistor, a pH sensor, and a gelled electrolyte. The electrode has a bendable joint which allows the user to adjust the positioning of the electrode prior to or during use and which facilitates electrode removal after chronic insertion. The glass stem is pointed to allow direct insertion into tissues. In a preferred embodiment, the glass stem is made of lead glass.